1. Field of the Invention
This invention relates to methods and controllers that monitor and limit concentration of carbon dioxide emitted by air heaters in an enclosed space, and, in particular, a manner of measuring and controlling the concentration to provide accurate data to the controller to maintain or limit proper levels of carbon dioxide concentration in a building space without use of expensive carbon dioxide monitors.
2. Description of the Related Art
The National Standard for Direct Fired Recirculating Industrial Air Heaters (ANSI Z83.18) sets standards for the concentration of carbon dioxide (CO2) that is permitted to be emitted from a recirculating direct gas-fired modulating air heater in an enclosed space. Related art systems typically use a CO2 sensor to determine the amount of CO2 that is being emitted by the air heater in an enclosed space. However, this approach is often problematic, as the accuracy of the sensor can be affected by the altitude, humidity, and location of the sensor, thus providing an inaccurate concentration of CO2 emitted from the heater in any enclosed space.
U.S. Pat. No. 6,431,457 (the '457 patent) discloses an air heater control system that controls temperature rise through a burner to limit the concentration of CO2 without the use of a CO2 sensor. Temperature rise through the burner is limited by the formula ΔT=Actual % OA*Pmax/19.63/k, where ΔT is the temperature rise, Actual % OA is the actual proportion of outside air that is brought through the burner, Pmax is the allowable concentration of CO2 in parts per million, and k is a factor based on the type of fuel burned by the burner.
There remains an opportunity to provide a method of determining a concentration of CO2 without the use of expensive CO2 sensors and without knowing the actual proportion of outside air that is brought through the burner.